Damage affecting pip-fruit trees in particular but also many other crops is likely as a result of adverse weather; particularly from hailstorms. One severe hailstorm, not an infrequent event, can totally destroy a crop and hence the income from it, or damage a crop by bruising so that it is downgraded to a less remunerative grade.
Other damage by wind, bats, insects, birds, frost and the like is also a perennial problem for gardeners and horticulturists, and while it is possible to put up or grow windbreaks to catch horizontal winds these have no effect on vertically oriented hazards like hailstones. One could build a roof over the crop, but this is expensive and furthermore as it is desirable to retract the protection when not required, a constructed roof is inappropriate. Retraction aids in protecting the structure itself during winds and snow, and lets more light, and desirable insects such as bees arrive at the plants below.
Plants respond to an improved environment but the optimum environment for a given plant changes with the weather, the time of day, and over the seasons. Hail protection for example is important when fruit is developing, but is not needed over winter. In winter, snow (to take one example) could overload a structure arranged to catch hail. To avoid these types of overloads, and to be able to modify the environment on a seasonal or dally basis if useful in particular circumstances, it is useful to be able to take away or re-install the generally horizontal canopies now used to provide sun, hail, bird, insect or wind protection.